This invention relates to a manual pushbutton keyboard system for an electronic pocket calculator, for a pushbutton telephone, or for other electrical or electronic appliances, and it is particularly concerned with such a keyboard which utilizes dished or domed discs as switch actuating elements of single-pole, single-throw (SPST) momentary switches for the keyboard.
More generally, calculator keyboards conventionally include a plurality of SPST momentary switches and a network of conductor paths on a printed circuit board leading to terminals at one margin of the board for connection of the keyboard switches to other electronic components, such as to various solid state, integrated circuit, and semi-conductor logic components within a calculator. Prior art keyboards, such as shown in the coassigned U.S. Pat. Nos. 3,684,842, 3,806,673 and 3,808,384, utilized domed discs as switch actuating elements. Use of such domed discs is desirable for various reasons including the tactile feedback the disc gives the operator when the disc suddenly moves from an unactuated position to an actuated position however in order to optimize this tactile feedback the outer peripheral margin of the disc must be higher than the inner contact so that the disc can move through the plane in which its margin lies. One way of providing different levels for the support of the disc and the inner contact is to mold the keyboard substrate having recesses formed therein so that the central surface portion of the board located beneath a respective disc will be at a lower level than the margin of the disc however providing such different levels makes it difficult and relatively costly to apply the required electrically conductive contacts and paths required. For instance, one known approach involves chemically etching metal from a laminated insulative board in a preselected pattern. This so-called subtractive method of producing a printed circuit board is relatively slow and expensive and it poses certain ecological problems in the disposal of chemical wastes. Additive electroless plating processes can be employed but recesses pose a problem in plating the vertical surfaces of the recesses so that special provisions must be made to avoid the problem.